English Colonies.—In Canada the coast lighting is in the hands of the minister of marine, and in most other colonies the public works departments have control of lighthouse matters.
Other Countries.—In Denmark, Austria, Holland, Russia, Sweden, Norway and many other countries the minister of marine has charge of the lighting and buoying of coasts; in Belgium the public works department controls the service.
In the Trinity House Service at shore lighthouse stations there are usually two keepers, at rock stations three or four, one being ashore on leave. When there is a fog signal at a station there is usually an additional keeper, and at electric light stations a mechanical engineer is also employed as principal keeper. The crews of light-vessels as a rule consist of 11 men, three of them and the master or mate going on shore in rotation.
The average annual cost of maintenance of an English shore lighthouse, with two keepers, is £275. For shore lighthouses with three keepers and a siren fog signal the average cost is £444. The maintenance of a rock lighthouse with four keepers and an explosive fog signal is about £760, and an electric light station costs about £1100 annually to maintain.
A light-vessel of the ordinary type in use in the United Kingdom entails an annual expenditure on maintenance of approximately £1320, excluding the cost of periodical overhaul.
Authorities.—Smeaton, Eddystone Lighthouse (London, 1793); A. Fresnel, Mémoire sur un nouveau system d’éclairage des phares (Paris, 1822); R. Stevenson, Bell Rock Lighthouse (Edinburgh, 1824); Alan Stevenson, Skerryvore Lighthouse (1847); Renaud, Mémoire sur l’éclairage et le balisage des côtes de France (Paris, 1864); Allard, Mémoire sur l’intensité et la portée des phares (Paris, 1876); T. Stevenson, Lighthouse Construction and Illumination (London, 1881); Allard, Mémoire sur les phares électriques (Paris, 1881); Renaud, Les Phares (Paris, 1881); Edwards, Our Sea Marks (London, 1884); D. P. Heap, Ancient and Modern Lighthouses (Boston, 1889); Allard, Les Phares (Paris, 1889); Rey, Les Progrès d’éclairage des côtes (Paris, 1898); Williams, Life of Sir J. N. Douglass (London, 1900); J. F. Chance, The Lighthouse Work of Sir Jas. Chance (London, 1902); de Rochemont and Deprez, Cours des travaux maritimes, vol. ii. (Paris, 1902); Ribière, Phares et Signaux maritimes (Paris, 1908); Stevenson, “Isle of May Lighthouse,” Proc. Inst. Mech. Engineers (1887); J. N. Douglass, “Beacon Lights and Fog Signals,” Proc. Roy. Inst. (1889); Ribière, “Propriétés optiques des appareils des phares,” Annales des ponts et chaussées (1894); Preller, “Coast Lighthouse Illumination in France,” Engineering (1896); “Lighthouse Engineering at the Paris Exhibition,” Engineer (1901–1902); N. G. Gedye, “Coast Fog Signals,” Engineer (1902); Trans. Int. Nav. Congress (Paris, 1900, Milan, 1905); Proc. Int. Eng. Congress (Glasgow, 1901, St Louis, 1904); Proc. Int. Maritime Congress (London, 1893); J. T. Chance, “On Optical Apparatus used in Lighthouses,” Proc. Inst. C.E. vol. xxvi.; J. N. Douglass, “The Wolf Rock Lighthouse,” ibid. vol. xxx.; W. Douglass, “Great Basses Lighthouse,” ibid. vol. xxxviii.; J. T. Chance, “Dioptric Apparatus in Lighthouses,” ibid. vol. lii.; J. N. Douglass, “Electric Light applied to Lighthouse Illumination,” ibid. vol. lvii.; W. T. Douglass, “The New Eddystone Lighthouse,” ibid. vol. lxxv.; Hopkinson, “Electric Lighthouses at Macquarie and Tino,” ibid. vol. lxxxvii.; Stevenson, “Ailsa Craig Lighthouse and Fog Signals,” ibid. vol. lxxxix.; W. T. Douglass, “The Bishop Rock Lighthouses,” ibid. vol. cviii.; Brebner, “Lighthouse Lenses,” ibid. vol. cxi.; Stevenson, “Lighthouse Refractors,” ibid. vol. cxvii.; Case, “Beachy Head Lighthouse,” ibid. vol. clix.; Notice sur les appareils d’éclairage (French Lighthouse Service exhibits at Chicago and Paris) (Paris, 1893 and 1900); Report on U.S. Lighthouse Board Exhibit at Chicago (Washington, 1894); Reports of the Lighthouse Board of the United States (Washington, 1852, et seq.); British parliamentary reports, Lighthouse Illuminants (1883, et seq.), Light Dues (1896), Trinity House Fog Signal Committee (1901), Royal Commission on Lighthouse Administration (1908); Mémoires de la Société des Ingénieurs Civils de France, Annales des ponts et chaussées (Paris); Proc. Inst. C. E.; The Engineer; Engineering (passim). (W. T. D.; N. G. G.)
LIGHTING. Artificial light is generally produced by raising
some body to a high temperature. If the temperature of a
solid body be greater than that of surrounding bodies it parts
with some of its energy in the form of radiation. Whilst the
temperature is low these radiations are not of a kind to which
the eye is sensitive; they are exclusively radiations less refrangible
and of greater wave-length than red light, and may be called
infra-red. As the temperature is increased the infra-red radiations
increase, but presently there are added radiations which
the eye perceives as red light. As the temperature is further
increased, the red light increases, and yellow, green and blue
rays are successively thrown off. On raising the temperature
to a still higher point, radiations of a wave-length shorter even
than violet light are produced, to which the eye is insensitive,
but which act strongly on certain chemical substances; these
may be called ultra-violet rays. Thus a very hot body in general
throws out rays of various wave-length; the hotter the body
the more of every kind of radiation will it throw out, but the
proportion of short waves to long waves becomes vastly greater
as the temperature is increased. Our eyes are only sensitive to
certain of these waves, viz. those not very long and not very
short. The problem of the artificial production of light with
economy of energy is the same as that of raising some body to
such a temperature that it shall give as large a proportion as
possible of those rays which the eye is capable of feeling. For
practical purposes this temperature is the highest temperature
we can produce. As an illustration of the luminous effect of the
high temperature produced by converting other forms of energy
into heat within a small space, consider the following statements.
If burned in ordinary gas burners, 120 cub. ft. of 15 candle gas
will give a light of 360 standard candles for one hour. The heat
produced by the combustion is equivalent to about 60 million
foot-pounds. If this gas be burned in a modern gas-engine,
about 8 million foot-pounds of useful work will be done outside
the engine, or about 4 horse-power for one hour. If this be used
to drive a dynamo for one hour, even if the machine has an
efficiency of only 80%, the energy of the current will be about
6,400,000 foot-pounds per hour, about half of which, or only
3,200,000 foot-pounds, is converted into radiant energy in the
electric arc. But this electric arc will radiate a light of 2000
candles when viewed horizontally, and two or three times as
much when viewed from below. Hence 3 million foot-pounds
changed to heat in the electric arc may be said roughly to
affect our eyes six times as much as 60 million foot-pounds
changed to heat in an ordinary gas burner.
Owing to the high temperature at which it remains solid, and to its great emissive power, the radiant body used for artificial illumination is usually some form of carbon. In an oil or ordinary coal-gas flame this carbon is present in minute particles derived from the organic substances with which the flame is supplied and heated to incandescence by the heat liberated in their decomposition, while in the electric light the incandescence is the effect of the heat developed by the electric current passed through a resisting rod or filament of carbon. In some cases, however, other substances replace carbon as the radiating body; in the incandescent gas light certain earthy oxides are utilized, and in metallic filament electric lamps such metals as tungsten or tantalum.
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| Fig. 1. |
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| Fig. 2.—Section of Reading Lamp. |
From the earliest times the burning of oil has been a source of light, but until the middle of the 19th century only oils of vegetable and animal origin were employed in indoor lamps for this purpose. Although many kinds were Vegetable and animal oils. used locally, only colza and sperm oils had any very extended use, and they have been practically supplanted by mineral oil, which was introduced as an illuminant in 1853. Up to the latter half of the 18th century the lamps were shallow vessels into which a short length of wick dipped; the flame was smoky and discharged acrid vapours, giving the minimum of light with the maximum of smell. The first notable improvement was made by Ami Argand in 1784. His burner consisted of two concentric tubes between which the tubular wick was placed; the open inner tube led a current of air to play upon the inner surface of the circular flame, whilst the combustion was materially improved by placing around the flame a chimney which rested on a perforated gallery a short distance below the burner. Argand’s original burner is the parent form of innumerable modifications, all more or less complex, such as the Carcel and the moderator.
A typical example of the Argand burner and chimney is represented in fig. 1, in which the burner is composed of three tubes, d, f, g. The tube g is soldered to the bottom of the tube d, just above o, and the interval between the outer surface of the tube g and the inner surface of the tube d is an annular cylindrical cavity closed at the bottom, containing the cylindrical cotton wick immersed in oil. The wick is fixed to the wick tube ki, which is capable
